1. Field of the Invention
This invention relates to an assembly for jetting, also known as non-contact dispensing, which is separate from and provides for different requirements on the assembly than contact dispensing such as screening.
2. Description of the Background Art
A prior art jetting machine is disclosed in copending patent application U.S. Ser. No. 09/719,237. Said patent application is focused on a certain part of the machine, which part is a new device for jetting droplets. The device comprises an eject chamber (37; 137) for containing a small volume of a viscous medium prior to the ejection thereof, an eject nozzle (36; 136) communicating with the eject chamber, eject means (22, 25; 122, 135) for rapidly ejecting said viscous medium from the eject chamber through said nozzle, and supply means for feeding said medium into the eject chamber. The supply means comprises a rotatably driven feed screw receiving the medium from a syringe containing the medium and forcing the medium towards the eject chamber. The medium contained within the syringe in turn is pressurised in order to force it out of the outlet of the syringe.
This prior art device works well. However, there is a problem involved in exchanging syringes in the device, particularly when the new syringe contains a different type of medium than the one to be exchanged. In the last mentioned case the operator of the machine has to rinse the portions of the device containing the medium. These portions are, inter alia, the eject chamber, the eject nozzle, and the feed screw. In the case of a non-contact dispensing machine, the rinse of the nozzle and the associated ejection parts is particularly important in order to achieve a good operation. While the rinse operation is performed the machine is stopped.
Another problem arising when exchanging syringes is that before resuming the production several dispensing operations must be performed, in order to refill the nozzle and the associated ejection parts with the new medium. Some extra ejections should be performed in order to guarantee that the medium is free from air bubbles. An attempt to reduce the exchange time is disclosed in JP-10294557. The time reduction is obtained by arranging a separate syringe holder at the machine. At the holder, a syringe which later on is to be substituted for the one presently used, is pressurised in that an amount of the medium is dispensed into a container. Thereby it is secured that the medium at the outlet of the syringe is free from air bubbles. Consequently, when replacing the syringe presently at use with the new one the application of medium onto a circuit board can be resumed immediately. However, this prior art solution is only useful in machines using the syringe for direct dispensing, and does not improve a machine of the jetting type to the same extent. Since such a machine has a separate ejecting mechanism, which receives the medium from the syringe, this ejecting mechanism still has to be refilled with the new medium before the application operation is resumed.
Consequently, the exchange of syringes causes an undesired fall in production. Additionally, the waste medium is generally environmentally hazardous and has to be carefully taken care of.
The object of this invention is to provide a solution to the above mentioned problems.
The invention, in one aspect thereof, provides for an assembly for jetting droplets of a viscous medium, said assembly being releasably mountable in a machine using the assembly for providing a substrate with deposits, and comprising a nozzle, an eject mechanism connected with the nozzle, a viscous medium container connected with the eject mechanism, and signal interface means.
By being releasably mountable the assembly is usable as a separate unit easily exchangeable and containing the medium. Consequently, the operator is relieved from the problem of handling the syringes and rinsing parts of the assembly. Additionally, the problem of handling the waste medium is eliminated. The assembly provides for a recycling system where the whole assembly, when empty of medium, is sent back to the supplier who originally delivered it.
For the purposes of this application, it is to be noted that the term xe2x80x9cdepositsxe2x80x9d should be interpreted as single or groups of viscous medium dots deposited on the substrate; the term xe2x80x9cviscous mediumxe2x80x9d should be interpreted as solder paste, flux, adhesive, conductive adhesive or any other kind of medium used for fastening components on the substrate; and that the term xe2x80x9csubstratexe2x80x9d should be interpreted as a printed circuit board (PCB), a substrate for ball grid arrays (BGA), chip scale packages (CSP), quad flat packages (QFP), and flip-chips or the like.
In another aspect thereof the invention provides for a machine for providing a substrate with deposits by jetting droplets of a viscous medium onto the substrate, comprising a docking device for receiving an assembly of the above described type, said docking device comprising an assembly support and complementary signal interface means.
In a further aspect thereof the invention provides for a docking device for receiving an assembly of the above described type, said docking device comprising an assembly support and complementary signal interface means.
The docking device facilitates the mounting/dismounting of the assembly at the machine by providing specific means, such as the assembly support and the interface means, simplifying the docking of the assembly. The mounting/dismounting is further facilitated by the assembly support comprising pneumatically operable assembly locking means, enabling a fast mounting/dismounting.
In accordance with another embodiment of the invention, there is provided an exchange assembly support for supporting at least one exchange assembly. By means of this support the invention is additionally improved by providing for an automatic exchange of assemblies at the docking device. Further, change over times are reduced due to the possibility of, while the machine is running, providing the exchange assembly support with new full assemblies, assemblies holding different types of paste, assemblies having different types of nozzles, etc., to be used later on by the machine.
In yet another aspect thereof, the invention provides for a method of exchanging and calibrating an assembly for jetting droplets of a viscous medium, said assembly being releasably mounted in a machine using the assembly for providing a substrate with deposits, and comprising an assembly holder having first holding means mating with an assembly support of a docking device of the machine, comprising the steps of:
exchanging the assembly for an exchange assembly;
moving the assembly to a calibration surface;
depositing a plurality of deposits on the calibration surface;
determining the position of said plurality of deposits by viewing it with a vision device comprised in the machine; and
determining an offset of the position from an expected position.
This method, which is possible to perform by means of inventive constructions according to the invention, that is the separate jetting assembly releasably mountable in a dispensing machine arranged for receiving such an assembly, is advantageous in that the operator of the machine does not have to deal with the assembly exchanges online. The steps of calibration assure that the new assembly is correctly mounted and that the accuracy of the dispensing process will be high.
Further objects and advantages of the present invention will be discussed below by means of exemplary embodiments.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modification within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.